As used in this specification, the following terms have the meanings ascribed to them below.
"Fiber" or "fibers" means the basic element of fabric or other textile structures which is characterized by a length at least 100 times its diameter or width and made from a synthetic polymer matrix. The term "fiber" encompasses short length fibers (i.e., staple fibers) and fibers of indefinite length (i.e., continuous filaments).
"Multicomponent fiber" or "Multicomponent fibers" means fibers having at least two longitudinally co-extensive domains or components. These domains (or components) may differ in the identity of the polymer matrix, or in the type or amount of additives present in each domain, or in both the identity of the matrix and the additive level or identity.
"Bicomponent fiber" or "bicomponent fibers" means a multicomponent fiber having only two different longitudinally coextensive domains.
"Sheath/core fiber" or "sheath/core fibers" means multicomponent fibers having one or more outer domains that substantially surround at least one or more inward domain. An outer domain that substantially surrounds an inward domain abuts more than 50% of the inner domain's periphery.
"Nonaqueous liquid" means a material which is substantially free from water and is in the liquid state at conditions commonly found in buildings and other environments occupied by humans typically 50.degree.-110.degree. F.
Multicomponent fibers are known. Multicomponent fibers may be classified into one of at least three major classes. One class includes multicomponent fibers with the components differing from each other in the type of polymer matrix forming each component. Such fibers are described in, for example. U.S. Pat. No. 4,285,748 to Booker et al.
Another class of multicomponent fibers includes those with components differing in the level or type of additive in the components but where the matrix polymers are predominately the same or similar. An example of this type of multicomponent fiber is described in U.S. Pat. No. 5,019,445 to Sternlieb.
A further category of multicomponent fibers includes fibers with components differing in both the polymeric matrix material and the relative amount of additives or types of additives in each component. Examples of such multicomponent fibers are described in U.S. Pat. No. 3,803,453 to Hull; U.S. Pat. No. 4,185,137 to Kinkel; and U.S. Pat. No. 5,318,845 to Tanaka.
In certain circumstances during the manufacture of multicomponent fibers, significant concern is given to whether or not such fibers rill separate at the interface between components. One reason multicomponent fibers separate is due to the incompatibility of the components. Sometimes, it is desirable that the components separate at the interface between them. For example, the incompatibility principle can be used to make microfibers by fibrillating multicomponent fibers along the component interface thereby resulting in fibers of decreased size. To make such microfibers, therefore, the incompatibility of the components might be intentionally maximized.
In other circumstances, however, it is undesirable for the components to separate from each other. For these cases, care must be taken in selecting matrix polymers and additives to assure sufficient compatibility or, rather, to prevent so much incompatibility that the fibers delaminate when subjected to post-spinning stress, e.g., bending around a godet.
Methods for adding additives to fibers are known. For example, U.S. Pat. No. 5,308,395 to Burditt describes a liquid carrier for incorporation into polymeric resins. This patent describes the use of such carriers to make fibers but does not address multicomponent fibers.
Also, U.S. Pat. No. 5,364,582 to Lilly describes the use of a certain carrier to add polyoxyethylene alkylamine antistatic agents to monocomponent fibers. The carders may be an organic resin based composition containing surfactant and diluent.
Moreover, the ability to add additives directly to a fiber extrusion line without the necessity of storing and metering extremely dry additive-containing chip provides significant process and economic advantages. U.S. Pat. No. 5,236,645 to Jones describes an aqueous based system for adding additives directly to a fiber extrusion process. The aqueous portion is removed through a vent in the extruder so that water is not significantly present in the extruder output. However, the addition of aqueous mixes to polymer melts may sometimes significantly reduce the relative or intrinsic viscosity of the polymer. This is true, for example, with nylon 6 and, to a larger extent, with polyester. The loss in viscosity has a significant effect on yarn physical properties and the ability to successfully spin fibers.
Therefore, there remains a need for methods to add additives inline during the fiber extrusion process without requiring removal of water and without leading to incompatibility problems resulting in delamination at the interface between components.